Flue gas chilling



Patented Dec. 25, 1951 FLUE GAS CHILLING Hyman R. Davis, Jackson Heights, and Robert M.

Santaniello, Brooklyn, N. Y., assignors to The Lummus Company, New York, N. Y., a corporation of Delaware Application June s, 195o, serial No. 165,914

This invention relates to an improvement in a l method and apparatus for cooling ue gas. It is particularly adapted to be employed in connection with a solvent dewaxing operation wherein flue gas is used as a blanketing medium during filtration. l

, Due to the explosive nature of the solvents employed in these solvent dewaxing operations, it is common practice to use a blanket of cooled inert gas in various locations and particularly in the filtration equipment.v Dewaxing operations requirelarge volumes of flue gas and much of this gas must be cooled to temperatures below F. Accordingly, it is apparent that the problem of cooling this gas is one which is large in score. Further complications are added by virtue of the fact that the gas to be cooled generally contains water which crystallizes out as ice. Present practice is to use alternate heat exchangers, one being used for cooling while others are in various stages of de-icing. This of course necessitates proportionately large amounts of equipment, special controls, and in addition results in opera# tional difficulties.

lThe principal object of our invention is to provide an improved method and apparatus for the repeated chilling of flue gas by direct contact with solvent or solvent solutions wherein the temperature reduction is accomplished without the ice clogging formation. a

, Amore specific object of our invention is to provide a method and means for the direct contacting of relatively cold solvent or pressed oil solution with flue gas in a vortex wherein highly intimate mixing and heat transfer are obtained and in whichliquid is thrown out centrifugally. Further objects and advantages of our invention will appear from the following description of a preferred form of embodiment thereofas described in the following specication and as illustrated in the attached drawing in which:

Fig. 1 is a schematic outline of our improved liuc gas chilling system. Fig. 2 isan enlarged substantially central vertical cross-section of the contacting unit.

Fig. 3 is an enlarged horizontal cross-section along `lines 3--3 of Fig. 2. a

In carrying out the invention, the wax-bearing oil from a suitable source indicated at I0 is mixed with a suitable solvent liquid from line Il. This solvent liquid may comprise a light petroleum fraction such'as naphtha orother various organic liquids or mixtures therecf,rinc1uding alcohols, ketones, aldehydes, cyclic hydrocarbons, benzol o r its homologs, or derivatives of these var- 3 claims; (01.196-19) u ious materials. The solvent in line II` may preferably be acetone, benzol and toluol, or methylethyl-ketone, benzol and toluol.

The mixture of oil to be ldewaxed and the .solvent liquids are cooled to the desired ltration temperature in heat exchanger I3 and are thence introduced into iilter 'I 4 which may be of the continuous rotating drum type or other type having a closed body. The lter provides a rotating lil-v tration surface, not shown, which' collects precipitated wax thereon. This wax is removed by suitable means and discharged into the wax disI charge chamber I5.

Ordinarily the separated wax on the `iilter surf face is vacuum dried and then washed by means of a spray of suitable washing liquid. The cake, after washing, is again dried by the passage of cold'inert gas therethrough.l The inert or flue gas enters the filter through lines I2 and I6 and the nitrate-solvent, oil, and wash liquid are generally indicated as being removed through line Il although separate withdrawal conduits are cus,- tomarily provided. Y

The liquid products removed fromA lter I4 through line Il together with the inert gas contained therein, enter ltrate tank I8 in which there is a partial separation of liquid from vapor or gas. The saturated gas is removed by vacuum pump I9 and discharged through line 20 to cool ing tower 2|. In addition, fresh gas make-up may be introduced from line 22 such gas passing through vacuum pump I9 to cooling tower 2| along with the recycled gas.

' Filtrate from which the gas has been separated is drawn oi from tank I8 through line 23' by pump 2li, a part of the solvent being suitably heated in heat exchanger 25 and thence passed to the solvent recovery system 2t through line 29. In this system the oil and water are separated from the dry solvent, the -oil being drawn' olf at 21, the water at 28 and the dry solvent through line I I. The dry solventinay be returned through line II to constitute the originalsource of sol-` vent for the initial oil mixture. y

The solvent recovery system 26 is not intended to reflect any particular type of apparatus Vand it may include distillation columns or other ap-y paratus designed to effect the desired degree of separation. Makeup solvent may be added through line 48.

The wet, compressed, warm gas in line 20, which may have a temperature of about F.,

must, for proper operation of the lter I4. be'

cooled to below the freezing point of water and preferably below 0 F. In accordance with our invention we propose to use the apparatus generally shown in the application of Ward J. Bloomer, Serial No. 59,119, filed November 12, 1948, now Patent Number 2,560,072. Y

The particular apparatus for accomplishing the mixing is generally shown in Fig. 2 and consists of Va, hollow cylindrical tuyre 3i which is mounted in the deck 32. The tuyre consists of a wall, as for example sheet material having a series of blades 34 which are struck out from the wall after slitting, thereby forming narrow passages 33 which are preferably of an approximate tangential nature extending substantially along the entire side wall of the tuyre. The tuyre also has an imperforate bottom 35 which is conveniently surrounded by an open solvent pan or container 36 to which liquid is fed through line 38.

The upper portion of the tuyre includes Van imperforate portion 4l which terminates in a generallyupwardly, downwardly and outwardly curved lip 42, the radius of which should be not less than l@ inch for a tuyre of 8 diameter.

Due vto the angularity of the blades, a high velocity gas will set up a vortex within the tuyere having a low pressure center which will continuously carry the gases or vapors upward. It is found in addition that the highly moving vapors or gas passing over the liquid in the pan will entrain a very large` amount of liquid. The path of the vapors is thus largely circular within the tuyre with a 4balance between the centrifugal outward tendency of the vortex and the inward flow of the gas or vapor. f

By -suitably proportioning the length and diameter of the tuyre it is possible to get the desired time and intimacy of contact of thegases and liquid so that a substantially uniform temperature of mix is obtained at the discharge end ofthe tuyre.

rThe imperforate portion 4| of the tuyre tends to coalesce the liquid which then nows over the lip to a quiescent hydrocarbon zone to be discharged outwardly'and thence downwardly onto the deck 32. The vapors will move upwardly and outwardly away from the tuyre.

To establish the desired cooling ofthe gases in line 20 We drawn off from 15% to 25% of the filtrate from line 29 through line 31 and pass it to the pan 36 of tuyre 3l.

The .form of construction shown in tower 2i involves the use of multiple stages of vertical contacting; three stages are here shown. In this case the 'solvent in line 31 enters the tower 2l through the lines 38, 39 and 40 in parallel. The vapors'to be cooled enter the lower part of the tower' throughthe line 20 and pass upwardly through the tuyres in the three decks 32, 43 and 44 in' series, each deck having a tuyre of the type shown at 3l in Fig. 2. The liquid discharge from each deck is returned through the lines 45, 46and 41'to tank I8. The overhead gases discharge through line I6. 1 If desired, the liquid discharged onto the decks 32, 43 and 44 may be withdrawn into the lower part of 'the tower 2l where it may be accumulated before being passed to tank I8, or it may be passed to a separate accumulator. n

` There are unique technical advantages in contacting Athe vapors and solvent in an operation wherein the liquid enters the stages in parallel and thevapors pass in series through the suc*- dssive stages as is shown in the drawing.

Witl'ia feed of '1,654 pounds per hour of gas at IUI) 'FJ it 4was possible to cool this to -v5 F. by

utilizing 34,500 pounds per hour of a. pressed oil filtrate at 10 F. such filtrate being removed in part at 48 F. in line 45, in part at 25 F. in line 46, and the remainder at 5 in line 41. The amount of solvent removed at the three points is substantially the saine. During this operation, thesolvent absorbs about200 pounds of water, etc., from the gas.

If the process is conducted in the manner described, very favorable operation is obtained accompanied by a substantial saving in the cost of the equipment. For a given operation it is found necessary to use a-v tuyre tower of perhaps one foot in diameter, fourteen feet high, and containing three tuyre's. In comparison the packed tower designed to perform the same operation is three feet in diameter and thirty feet high and contains twenty feet of packing.

The high dispersion in the tuyre produces substantially equilibrium 'conditions (100% eiiciency) -a's opposed to 5075% efficiency in a packed tower. This' means that a closer temperature approach can be obtained and therefore smaller amounts of liquid can be used for cooling. Furthermore, the use of the ltrate according to this invention makes possible the velimination of a separate cooling `iiuid, an external pump andy cooler, and the accompanying refrigerating system.

When cooling to low temperatures in a packed tower, ice accumulates and interferes with operations. In the tuyre arrangement as shown in the drawing, there are no small openings in the contact vrzone wherein ice may accumulate; the relatively high velocity at the area of contact insures that any ice will be thrown out of the tuyre proper.

Aside from mechanical difliculties involved in the packed tower such as channelling and low efficiency, it is found that when a contacting operation such as hereinbefore described, is performed with a single liquid stream iiowing countercurrent to a gas stream, the desired results cannot be obtained in practical manner. If a single stream operation is plotted for example, in terms of temperature versus heat content of the dry gas and the operating and equilibrium lines laid out in the usual manner, it is readily observable that duer to the pinch near the saturation temperature of the gas (i. e. nearness of the operating and equilibrium lines)A a large number of transfer units is needed. For the cited example 15 transfer units would be required for the series operation whereas only 3 are required for the parallel operation.

It is of course to be understood that various automatic or semiautomatic controls will be used in addition to those that are shown. A principal feature however of our invention is the'establi'shing of a vortex within the tuyre, wherein the ascending gas may be directly contacted by liquid, and wherein said liquid is thereafter thrown out on discharge from the tuyre, with the substantially dry gas being returned tothe filter operation. AIt is our experience that the minimum velocity of--g-as for such purpose should be at least about 30 feet per 'second but veloci-V ties upto feet per second can be used with- Y eration as there is no reviviiication of apparatus necessary and each part of the unit operates at a substantially constant temperature which may be controlled to avoid heat loss. It will also be appreciated that the apparatus is simple, economical, and cheap to construct.

We claim:

l. In the process of separating wax from a chilled mixture of wax, oil, and solvent by filtration of said mixture in an atmosphere of chilled flue gas to produce a separated wax and a ltrate containing said flue gas, wherein saidiiuegas is separated from said -liltrate in a gas-liquid separating operation, and wherein make-up gas is introduced to said separated ue gas thereby forming a combined gas, the improved method of cooling and drying said combined gas in a multi-stage gas-liquid contacting operation which comprises forming in each of said stages a vortical path of said combined gas in a restricted zone in said stage, withdrawing liquid from said gas-liquid separating operation, dividing said liquid into a plurality of streams corresponding to said plurality of stages, directing each of said streams to the initial part of said vortical path in each of said stages, maintaining said liquid and said combined gas in said vortical path whereby said gas is cooled and dried, releasing said liquid from said gas upon discharge from said vortical path, withdrawing said dried and cooled gas from said vortical path, and passing said last-mentioned gas to subsequent stages wherein said gas is contacted with fresh feed in a manner similar to that in said first stage, said gas passing through said plurality of stages in series whereas said liquid passes therethrough in parallel, whereby said cooling operation is effected with a high eiTciency and a low total pressure drop through said plurality 0f stages.

2. In the process of claim 1, the improvements claimed therein where said combined gas is cooled to below 32 F. thereby freezing out water contained therein.

Iii)

6 3. In the process of separating wax from a. chilled mixture of wax, oil, and solvent by iiltration of said mixture in an atmosphere of chilled ue gas to produce a separ-ated wax and a lvtrate containing said flue gas, and wherein said flue gas is separated from said ltrate in a gasliquid separating operation, the improved method of cooling and drying said separated gas in a multi-stage gas-liquid contacting operation which comprises concurrently forming in each of said stages a vortical path of said separated gas in a restricted zone in said stage, withdrawing liquid from said gas-liquid separating operation, dividing said liquid into a plurality of streams corresponding to said plurality of stages, directing each of said streams to the initial part of said vortical path in each of said stages, maintaining said liquid and said separated gas in said vortical path whereby said separated gas is cooled and dried, releasing said liquid from said separated gas upon discharge from said vortical path, withdrawing said dried and cooled gas from said vortical path, and passing said last-mentioned gas to subsequent stages wherein said gas is contacted with fresh feed in a manner similar to that in said first stage, said gas passing through said plurality of stages in series whereas said liquid passes therethrough in parallel, whereby said cooling operation is effected with a high efficiency and a low total pressure drop through said plurality of stages.

I-IYMAN R. DAVIS.

ROBERT M. SANTANIELLO.

REFERENCES CITED The following references are of record in the die of this patent:

UNITED STATES PATENTS Numher Name Date 971,297 Miles Sept. 27, 1910 1,724,513 Pollitzer Aug. 13, 1929 2,189,491 Hawley Feb. 6, 1940 2,511,190 Wright June 13, 1950 

1. IN THE PROCESS OF SEPARATING WAX FROM A CHILLED MIXTURE OF WAX, OIL, AND SOLVENT BY FILTRATION OF SAID MIXTURE IN AN ATMOSPHERE OF CHILLED FLUE GAS TO PRODUCE A SEPARATED WAX AND A FILTRATE CONTAINING SAID FLUE GAS, WHEREIN SAID FLUEGAS IS SEPARATED FROM SAID FILTRATE IN A GAS-LIQUID SEPARATING OPERATION, AND WHEREIN MAKE-UP GAS IS INTRODUCED TO SAID SEPARATED FLUE GAS THEREBY FORMING A COMBINED GAS, THE IMPROVED METHOD OF COOLING AND DRYING SAID COMBINED GAS IN A MULTI-STAGE GAS-LIQUID CONTACTING OPERATION WHICH COMPRISES FORMING IN EACH OF SAID STAGES A VORTICAL PATH OF SAID COMBINED GAS IN A RESTRICTED ZONE IN SAID STAGE, WITHDRAWING LIQUID FROM SAID GAS-LIQUID SEPARATING OPERATION, DIVIDING SAID LIQUID INTO A PLURALITY OF STREAMS CORRESPONDING TO SAID PLURALITY OF STAGES, DIRECTING EACH OF SAID STREAMS TO THE INITIAL PART OF SAID VORTICAL PATH IN EACH OF SAID STAGES, MAINTAINING SAID LIQUID AND SAID COMBINED GAS IN SASID VORTICAL PATH WHEREBY SAID GAS IS COOLED AND DRIED, RELEASING SAID LIQUID FROM SAID GAS UPON DISCHARGE FROM SAID VORTICAL PATH, WITHDRAWING SAID DRIED AND COOLED GAS FROM SAID VORTICAL PATH, AND PASSING SAID LAST-MENTIONED GAS TO SUBSEQUENT STAGES WHEREIN SAID GAS IS CONTACTED WITH FRESH FEED IN A MANNER SIMILAR TO THAT IN SAID FIRST STAGE, SAID GAS PASSING THROUGH SAID PLURALITY OF STAGES IN SERIES WHEREAS SAID LIQUID PASSES THERETHROUGH IN PARALLEL, WHEREBY SAID COOLING OPERATION IS EFFECTED WITH A HIGH EFFICIENY AND A LOW TOTAL PRESSURE DROP THROUGH SAID PLURALITY OF STAGES. 